Glass foams can be made from pre-formulated feedstocks. For example, a typical glass feedstock contains sodium silicate. Aqueous sodium silicate is known to display intumescence and/or volume expansion upon heating. However, sodium silicate is generally water-soluble, and foam products resulting from sodium silicate often display poor chemical durability. It is possible to make a more chemically durable glass foam by using glass particles, such as recycled, ground glass known in the industry as “cullet,” and adding additional materials, such as an external or additional blowing agent (e.gs., sodium carbonate, calcium carbonate, calcium sulfate, carbon, sugar, and the like) and a binder.
However, obtaining a glass feedstock typically involves a process that requires high temperatures for melting the raw materials and long residence times. For example, a typical glass feedstock includes a physical mixture of virgin raw materials and, optionally, cullet. The virgin raw materials contain quartz sand (crystalline SiO2) and other ingredients, such as soda ash (Na2CO3) and limestone (CaCO3) for soda-lime-silica glass, for example, and the cullet primarily contains shards of glass from previously-formed consumer or commercial glass products that are consistent with the desired characteristics of the final glass product.
The residence time and temperatures required to melt conventional glass feedstock in the glass furnace are relatively long and high, respectively. The melting of the glass feedstock can be made less taxing if some of the virgin raw materials are replaced with cullet in the feedstock. But cullet is not widely available as a commodity in some regions and, even if it is, bulk purchases of the recycled material are subject to great variations in color and other characteristics that may restrict glass manufacturing options.